An elastic mount is typically used to hold the steering mechanism, engine, and like parts of a motor vehicle on the frame thereof. Usually an inner part or member such as a pin is fitted through a hole in an elastomeric body of revolution which is itself received in an outer part or member constituted by an eye formed in or carried on the motor-vehicle frame. Such a mount must be able to withstand radially direct forces without substantial deformation, as when, for instance, acting as an axle mount to insure accurate guiding of the axle. In addition such a mounts must have a long service life, a requirement that is particularly hard to meet since the constant oscillations to which it is subjected constitute a considerable strain. It is for this reason that mounts of rubber or a similar elastomer and metal are typically used since the relative motions of the inner part and the outer part are translated into only molecular deformation in the elastomer rather than sliding of surfaces relative to each other. In addition such a mount has the advantage that it is always operational and completely silent. As a rule such elastic mounts employing molecular deformation only are formed as hollow cylindrical sleeves as well as conical, rodlike, semicircle, or spherical mounts.
In such elastic mounts it is necessary that the elastomeric body, which is made of so-called constant-volume material, not be pressed outwardly by radial forces, and it also should not be extruded axially by such forces. If this is allowed to occur radial wall thickness of the elastomeric body decreases so that the inner part will not be centered within the outer part and, for example in an axle mount, the inner part will become misaligned. In addition considerable shifting of the rubber on the metal creates wear and rapid destruction of the rubber. This lateral shifting of the rubber is eliminated in known mounts by vulcanizing to both inner surface and the outer surface of the body a respective metal sleeve that extends over the complete inner and outer surfaces of the elastomeric body and prevent any extrusion from these surfaces.
It is known to prestress these mounts by forcing the unstressed elastomeric body between a pair of metal sleeves, the outer sleeve being of lesser inner diameter than the outer diameter of the body and the inner sleeve being of greater outer diameter in the inner diameter of the body. This prestressing creates a pressure in the body which is proportional to the modulus of elasticity thereof and orients the molecules of the elastomer so as to equalize the stresses in the body. Such precompression increases the rigidity and strength of the mount. The difficulty, however, with such arrangements is that the elastomeric body can still slide relative to the sleeves in which it is mounted. In addition it is necessary that the inner dimensions of the outer part in which the mount is to be secured be exact so as to fit the outer sleeve, and that outer dimensions of the inner part be similarly precise. As a rule the inner sleeve is clamped in place by bolt arrangements so as to prevent shifting of this inner sleeve relative to the central body. Not only is such a mount extremely difficult to remove and replace, but the bolting of the inner sleeve adds expense to the construction of the arrangement.
It is also known to vulcanize the elastic body in place between the inner and outer sleeves. To this end the inner sleeve and the outer sleeve are usually split so as to permit their diameters to be changed in order to prestress the body. In such an arrangement it is almost invariably necessary to machine the sleeves of the mount after they are vulcanized to the rubber. In addition all of the difficulties of fitting the composite unit into the two parts are still present.
Another arrangement is known using a one-piece inner sleeve and an outer sleeve composed of several segments which are all vulcanized to the body and which, when pressed together, prestress the body. The body is split between the segments so that when they are pressed together the splits close and a prestressed assembly is formed. Such a mount is relatively expensive to manufacture.
Thus the known mounts typically have several difficulties. First of all they are relatively expensive to manufacture, as their metal parts must be made to close tolerances so that they must be produced in several different steps. It is necessary that the elements or parts in which or into which such a mount is fitted also be built to close tolerances and frequently provided with supplementary holding devices. Such devices can frequently slip relative to the parts on which they are mounted so as to become relatively ineffective. Furthermore it is usually impossible to remove such a motor mount without destroying it, so that a new mount must be provided each time the assembly is taken apart.